Relay station apparatus, mobile communication system, base station apparatus, and method for controlling relay station

ABSTRACT

A mobile communication system includes at least one upper radio station ( 1 ) and a relay station ( 2 ). The relay station ( 2 ) performs a radio relay between a lower radio station ( 3 ) and the upper radio station ( 1 ). The relay station ( 2 ) is configured to attach, when an attaching to a first upper radio station included in attaching configuration information indicating an upper radio station to which the relay station ( 2 ) should attach is unsuccessful, to a second upper radio station different from the first upper radio station, and to notify a network ( 4  and  5 ) of notification information via the second upper radio station, the notification information indicating that the attaching to the first upper radio station is unsuccessful.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. patent application Ser. No.13/813,855, filed on Feb. 1, 2013, which is a National Stage ofInternational Application No. PCT/JP2011/002708, filed on May 16, 2011,which claims priority from Japanese Patent Application No. 2010-174455,filed on Aug. 3, 2010, the contents of all of which are incorporatedherein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a system including a base station and arelay station attaching to the base station.

BACKGROUND ART

In LTE-Advanced (Long Term Evolution Advanced) of 3GPP (3rd GenerationPartnership Project), the introduction of relay stations (hereinafter“RNs (Relay Nodes)”) is under review (see Non Patent Literature 1). TheRN is one of techniques for increasing the communication speed of mobilestations (hereinafter “UEs (User Equipments)”) located at cell edges andfor increasing cell areas of base stations (hereinafter “eNBs (EvolvedNode Bs)”), for example. The details of the RN architecture, which isunder review in 3GPP, are disclosed in Non Patent Literature 2.

The outline of an RN system based on the RN architecture disclosed inNon Patent Literature 2 will be described below. FIG. 1 is a diagramshowing a network configuration example when the RN of 3GPP is used. Abase station (eNB) 1 belongs to a core network (hereinafter “CN”) 4 of amobile communication network operator. The CN 4 includes a mobilitymanagement entity (hereinafter “MME”) and a serving gateway (hereinafter“S-GW”). The eNB 1 generates an eNB cell 10 and relays traffic between amobile station (UE) 3 and the CN 4. A relay station (RN) 2 attaches tothe eNB 1 by means of a backhaul link (BL1 in the figure). The UE 3attaches to the eNB 1 or the RN 2 by means of an access link (AL1 or AL2in the figure). The RN 2 attaches to the CN 4 through the backhaul link(BL1) with the eNB 1. The RN 2 generates an RN cell 20 and relaystraffic between the UE 3 and the CN 4. An OAM server 5 manages theinstallation position of the eNB 1, and the cell information (usefrequency, Physical Cell ID (PCI), and the like) of the eNB cell 10. Thebackhaul link and the access link will be explained later.

FIG. 2 is a diagram showing a sequence when an RN attaches to an eNB anda CN and starts an RN cell operation. The RN establishes a networkconnection in an operation (hereinafter “UE mode”) similar to that of anexisting UE upon initial start-up (step S1). Specifically, the RNconfigures a Radio Resource Control (hereinafter “RRC”) connection withthe eNB. When the process for the RN to attach to the eNB and the CN inthe UE mode is completed, the RN transitions to an operation mode as anetwork node (hereinafter “RN mode”), and operates the RN cell. When theRN transitions to the RN mode, a method of controlling the backhaul linkis also switched from the UE mode to the RN mode (step S2).

In a network introducing the RN, the eNB that supports the RN mode isreferred to as “Donor eNB (hereinafter “DeNB”)”. Herein, only in thecase of describing matters unique to the DeNB related to the connectionwith the RN, the term “DeNB” is used to be distinguished from a normaleNB. Further, herein, the UE (for example, UE 3-1 in FIG. 1) thatattaches to the DeNB is referred to as “eNB-UE”. On the other hand, theUE (for example, UE 3-2 in FIG. 1) that directly attaches to the RN isreferred to as “RN-UE”. Furthermore, in the case of describing matterscommon to the eNB-UE and the RN-UE, the term “UE” is simply used.

In a discussion about the RN in the 3GPP, there is a demand forsupporting a multihop RN in the future. The multihop RN is a techniquethat makes it possible to connect an additional RN to an RN thatattaches to a DeNB in a cascade configuration. Herein, in the case ofdescribing the multihop, an RN that attaches to a lower layer of a DeNBwith a radio interface is referred to as “upper RN”, and an RN thatattaches to a lower layer of the upper RN is referred to as “lower RN”so as to distinguish the RNs from each other. Additionally, herein,radio interfaces between a DeNB and an RN and between an upper RN and alower RN are called “backhaul links”. Meanwhile, radio interfacesbetween an eNB and an eNB-UE and between an RN and an RN-UE are called“access links”.

Furthermore, in the discussion about the RN in the 3GPP, it is assumedthat the RN holds, as attaching configuration information, cellinformation of a DeNB cell to which the RN can attach (see Non PatentLiterature 3). The attaching configuration information includesinformation for designating a donor base station, a cell, or a sector towhich the RN should attach. Specifically, the attaching configurationinformation includes a frequency of a DeNB cell and a Physical Cell ID(PCI), for example. The RN specifies the DeNB to which the RN shouldattach, based on the attaching configuration information.

CITATION LIST Non Patent Literature

-   [Non Patent Literature 1] 3GPP TR36.912 V9.2.0 (2010-03),    “Feasibility study for Further Advancements for E-UTRA    (LTE-Advanced)”-   [Non Patent Literature 2] 3GPP TR36.806 V9.0.0 (2010-03), “Relay    architectures for E-UTRA (LTE-Advanced)”-   [Non Patent Literature 3] 3GPP R2-101951 Report of 3GPP TSG RAN WG2    meeting #69, March, 2010

SUMMARY OF INVENTION Technical Problem

The contents of the attaching configuration information to be held bythe RN may be different for each RN depending on the installed locationof the RN and the policy of a communication carrier. Accordingly, anoperator has to set the attaching configuration information inconsideration of the installed location of the RN and the policy of thecommunication carrier for each RN. These operations are actuallydifficult, and there is a problem of an increase in costs such asCapital Expenditure (CAPEX) and Operational Expenditure (OPEX).

The present invention has been made in view of the above-mentionedproblems, and an object of the invention is to provide a mobilecommunication system, a relay station apparatus, a base stationapparatus, a method for controlling a relay station, and a program,which contribute to simplification of setting of attaching configurationinformation in a system where a relay station (RN) attaches to a donorbase station (DeNB) based on attaching configuration information.

Solution to Problem

In a first aspect of the present invention, a relay station apparatusincludes a lower radio link communication unit, an upper radio linkcommunication unit, and a control unit. The lower radio linkcommunication unit is configured to perform radio communication with atleast one lower radio station. The upper radio link communication unitis configured to perform radio communication with at least one upperradio station. The control unit is configured to attach, when anattaching to a first upper radio station included in attachingconfiguration information indicating an upper radio station to which therelay station apparatus should attach is unsuccessful, to a second upperradio station different from the first upper radio station, and tonotify a network of notification information indicating that theattaching to the first upper radio station is unsuccessful.

In a second aspect of the present invention, a mobile communicationsystem includes at least one upper radio station, and a relay stationthat performs a radio relay between a lower radio station and an upperradio station. The relay station is configured to attach, when anattaching to a first upper radio station included in attachingconfiguration information indicating an upper radio station to which therelay station should attach is unsuccessful, to a second upper radiostation different from the first upper radio station, and to notify anetwork of notification information via the second upper radio station,the notification information indicating that the attaching to the firstupper radio station is unsuccessful.

In a third aspect of the present invention, a base station apparatusincludes a radio communication unit and a control unit. The radiocommunication unit is configured to perform radio communication with amobile station and a relay station. The control unit controlscommunication with the relay station. When the base station apparatusdoes not correspond to an upper station preliminarily determined as adestination to which the relay station attaches, the control unitcontrols the radio communication unit to connect to the relay station byusing a first connection mode in which the relay station operates as amobile station. Further, when the base station apparatus corresponds tothe upper station, the control unit controls the radio communicationunit to connect to the relay station by using a second connection modein which the relay station operates as a relay station.

In a fourth aspect of the present invention, a method for controlling arelay station that is wirelessly connectable to an upper radio stationincludes the following steps of:

(a) attaching, when an attaching to a first upper radio station includedin attaching configuration information indicating an upper radio stationto which the relay station should attach is unsuccessful, to a secondupper radio station different from the first upper radio station; and

(b) notifying a network of notification information via the second upperradio station, the notification information indicating that theattaching to the first upper radio station is unsuccessful.

In a fifth aspect of the present invention, a program causes a computerto execute the method according to the fourth aspect of the presentinvention described above.

In a sixth aspect of the present invention, a relay station apparatusincludes a lower radio link communication unit, an upper radio linkcommunication unit, and a control unit. The lower radio linkcommunication unit is configured to perform radio communication with atleast one lower radio station. The upper radio link communication unitis configured to perform radio communication with at least one upperradio station. The control unit is configured to determine whetherattaching configuration information indicating an upper radio station towhich the relay station apparatus should attach is held or not, and toattach to an upper radio station included in the attaching configurationinformation acquired from a network according to a result of thedetermination.

In a seventh aspect of the present invention, a mobile communicationsystem includes at least one upper radio station, and a relay stationthat performs a radio relay between a lower radio station and an upperradio station. Here, the relay station is configured to determinewhether attaching configuration information indicating an upper radiostation to which the relay station should attach is held or not, and toattach to an upper radio station included in the attaching configurationinformation acquired from a network according to a result of thedetermination.

In an eighth aspect of the present invention, a method for controlling arelay station that is wirelessly connectable with an upper radio stationincludes the steps of:

(a) determining whether attaching configuration information indicatingan upper radio station to which the relay station should attach is heldor not; and

(b) attaching to an upper radio station included in the attachingconfiguration information acquired from a network according to a resultof the determination.

In a ninth aspect of the present invention, a program causes a computerto execute the method according to the eighth aspect of the presentinvention described above.

Advantageous Effects of Invention

According to the present invention, it is possible to provide a mobilecommunication system, a relay station apparatus, a base stationapparatus, a method for controlling a relay station, and a program,which contribute to simplification of setting of attaching configurationinformation in a system in which a relay station (RN) attaches to adonor base station (DeNB) based on attaching configuration information.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a configuration of a typical mobilecommunication system;

FIG. 2 is a diagram showing a sequence when an RN attaches to a DeNBaccording to the background art;

FIG. 3 is a block diagram showing a configuration of a mobilecommunication system according to first to fifth embodiments;

FIG. 4 is a block diagram showing a configuration example of a basestation 1;

FIG. 5 is a block diagram showing a configuration example of a relaystation 2;

FIG. 6 is a block diagram showing a configuration example of a mobilestation 3;

FIG. 7 is a block diagram showing a configuration example of an OAMserver 5;

FIG. 8 is a sequence diagram showing an example of a procedure fornotifying a state of attaching configuration information in the firstembodiment of the invention;

FIG. 9 is a flowchart of the relay station 2 in the first embodiment ofthe invention;

FIG. 10 is a flowchart of the OAM server 5 in the first, second, andfifth embodiments of the invention;

FIG. 11A is a sequence diagram showing an example of a procedure fornotifying a state (validity) of attaching configuration information inthe second embodiment of the invention;

FIG. 11B is a sequence diagram showing an example of a procedure fornotifying a state (validity) of attaching configuration information inthe second embodiment of the invention;

FIG. 12 is a flowchart of the relay station 2 in the second embodimentof the invention;

FIG. 13 is a sequence diagram showing an example of a procedure fornotifying a state (availability) of attaching configuration informationin the third embodiment of the invention;

FIG. 14 is a flowchart of the relay station 2 in the third embodiment ofthe invention;

FIG. 15 is a flowchart of the OAM server 5 in the third and fourthembodiments of the invention;

FIG. 16A is a sequence diagram showing an example of a procedure fornotifying a state of attaching configuration information in the fourthembodiment of the invention;

FIG. 16B is a sequence diagram showing an example of a procedure fornotifying a state of attaching configuration information in the fourthembodiment of the invention;

FIG. 17 is a flowchart of the relay station 2 in the fourth embodimentof the invention;

FIG. 18A is a sequence diagram showing an example of a procedure fornotifying a state of attaching configuration information in the fifthembodiment of the invention;

FIG. 18B is a sequence diagram showing an example of a procedure fornotifying a state of attaching configuration information in the fifthembodiment of the invention;

FIG. 19 is a flowchart of the relay station 2 in the fifth embodiment ofthe invention; and

FIG. 20 is a flowchart of the base station 1 in the fifth embodiment ofthe invention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the drawings. In the drawings, the sameelements are denoted by the same reference numerals, and a repeatedexplanation is omitted as needed for clarity of the explanation.

First Embodiment

In a first embodiment, an RN temporarily attaches to an eNB and notifiesan upper network apparatus, such as an OAM server, of a state ofattaching configuration information. The notification of the state, forexample, includes (i) information indicating a correspondence relationbetween a donor base station designated by the attaching configurationinformation and a currently attaching base station, (ii) informationindicating whether valid attaching configuration information is held ornot, or (iii) a request for new attaching configuration information.

FIG. 3 is a diagram showing a configuration example of a radiocommunication system including a base station 1, a relay station 2, amobile station 3, and a core network 4 according to this embodiment.This embodiment will be described assuming that the radio communicationsystem is an FDD (Frequency division Duplex)-OFDMA, more specifically, aradio communication system of LTE-Advanced based on LTE. The basestation 1 belongs to the core network 4 of a mobile communicationnetwork operator, and relays traffic between the mobile station 3 andthe core network 4. The base station 1 is able to accommodate the relaystation 2, and also the mobile station 3.

FIG. 4 is a block diagram showing a configuration example of the basestation 1. Referring to FIG. 4, a radio communication unit 11 generatesa downlink signal by performing processing, such as mapping ontoresource elements, OFDM signal generation (IDFT: Inverse DiscreteFourier Transform), frequency conversion, and signal amplification, on atransmission symbol sequence of a physical channel supplied from atransmit data processing unit 12. The generated downlink signal iswirelessly transmitted from an antenna. The radio communication unit 11receives an uplink signal transmitted from the mobile station 3 or therelay station 2, and restores a reception symbol sequence.

The transmit data processing unit 12 stores the data for the mobilestation 3 or the relay station 2, which is acquired from a communicationunit 14, in buffers set for each mobile station and for each bearer, andgenerates a transport channel by performing error correction coding,rate matching, interleaving, or the like. Further, the transmit dataprocessing unit 12 adds control information to data sequence of thetransport channel to generate a radio frame. Furthermore, the transmitdata processing unit 12 generates a transmission symbol sequence foreach physical channel by performing scrambling and modulation symbolmapping on the data sequence of the radio frame.

A received data processing unit 13 restores the received data for eachlogical channel from the reception symbol sequence supplied from theradio communication unit 11. User traffic data included in the obtainedreceived data and a part of control data are transferred to the corenetwork 4 via the communication unit 14.

A relay node control unit 15 controls the transmission timing and radioresource allocation related to the data to be transmitted to the mobilestation 3 and the relay station 2. Further, the relay node control unit15 receives information indicating whether to support an RN operation(corresponding to an RN mode), which is notified from the relay station2, via the received data processing unit 13. The relay node control unit15 performs configuration of a backhaul link according to whether therelay station 2 supports the RN operation.

FIG. 5 is a block diagram showing a configuration example of the relaystation 2. The relay station 2 has a function equivalent to the basestation 1, unless explicitly specified otherwise. Referring to FIG. 5, alower radio link communication unit 21 receives the uplink signaltransmitted from the mobile station 3 via the antenna. A received dataprocessing unit 23 has a function equivalent to the received data unit13 of the base station 1, and the obtained received data is transmittedto the base station 1 via an upper radio link communication unit 24. Atransmit data processing unit 22 has a function equivalent to thetransmit data processing unit 12 of the base station 1, and generates atransmission symbol sequence from the transmit data which is acquiredfrom the upper radio link communication unit 24 and transmitted to themobile station 3. The lower radio link communication unit 21 generates adownlink signal from the symbol sequence and transmits the downlinksignal to the mobile station 3.

An attaching configuration information control unit 25 controls theattaching configuration information related to the base station 1. Theattaching configuration information control unit 25 receives theattaching configuration information from the base station 1 or the corenetwork 4 via the upper radio link communication unit 24 and thetransmit data processing unit 22. Specifically, the attachingconfiguration information control unit 25 notifies an OAM server 5 ofthe state of the attaching configuration information. For example, theattaching configuration information control unit 25 determines validityof the attaching configuration information based on whether information(a frequency of a DeNB cell, a Physical Cell ID (PCI), or the like) ofthe base station to which the relay station 2 actually attaches matchesinformation on a donor base station, a cell, or a sector which isdesignated by predetermined attaching configuration information and towhich the relay station should attach. The attaching configurationinformation control unit 25 notifies the OAM server 5 of thedetermination result. The notification of this case may includeinformation indicating whether the attaching configuration informationis correct or not. The notification of this case may include informationcapable of determining whether the base station to which the relaystation actually attaches corresponds to the donor base station to whichthe relay station should attach.

For example, the attaching configuration information control unit 25 maynotify the OAM server 5 that the relay station 2 does not hold theattaching configuration information. The notification of this case mayinclude information capable of determining that the relay station 2 doesnot hold the attaching configuration information. The notification ofthis case may also include a request message of new attachingconfiguration information. For example, when the relay station 2 holdsthe attaching configuration information but the attaching configurationinformation is unavailable due to expiration or the like, the attachingconfiguration information control unit 25 may notify the OAM server 5that the available attaching configuration information is not held. Thenotification of this case may include information capable of determiningthat the relay station 2 does not hold the available attachingconfiguration information.

FIG. 6 is a block diagram showing a configuration example of the mobilestation 3. A radio communication unit 31 receives a downlink signal viaan antenna. A received data processing unit 32 sends received datarestored from the received downlink signal to a buffer unit 35. Thereceived data stored in the buffer unit 35 is read out and useddepending on the purpose thereof. A transmit data control unit 33, atransmit data processing unit 34, and the radio communication unit 31generate an uplink signal by using the transmit data stored in thebuffer unit 35, and transmit the signal to the base station 1 or therelay station 2.

FIG. 7 is a block diagram showing a configuration example of the OAMserver 5. The OAM server 5 includes a communication unit 51 thatperforms communication with the core network 4, a transmit dataprocessing unit 52, a received data control unit 53, and an attachingconfiguration information management unit 54. The received dataprocessing unit 53 receives data transmitted from the relay station 2.When the received data includes a notification as to the state of theattaching configuration information of the relay station 2 or a requestof attaching configuration information, the received data is transferredto the attaching configuration information management unit 54. Theattaching configuration information management unit 54 judges whether ornot to notify the relay station 2 of the attaching configurationinformation, and sends the attaching configuration information from thetransmit data processing unit 52 to the relay station 2 based on thejudgment result.

Subsequently, a specific example of a procedure for notifying the stateof the attaching configuration information according to the firstembodiment will be described with reference to FIGS. 8 to 10.

FIG. 8 is a sequence diagram showing an example of a procedure fornotifying the state of the attaching configuration information accordingto the first embodiment. FIG. 8 shows interactions among the OAM server5, the core network 4, the base station 1, and the relay station 2. InFIG. 8, “OAM” corresponds to the OAM server 5; “MME” corresponds to thecore network 4; “DeNB” corresponds to the base station 1; and “RN”corresponds to the relay station 2.

In step S101, the RN searches for the eNB to which the RN attaches, andperforms configuring an RRC connection to the detected eNB (step S102).After configuring the RRC connection, the RN performs network attachingprocedure to the core network with the MME (step S103), and shifts toprocessing of bearer setup with the MME (step S104). In step S104, abearer setup procedure is performed between the MME and the eNB. In stepS105, a bearer setup procedure is performed between the eNB and the RN.After completion of the processing of steps S104 and S105, the RN cancommunicate with the OAM. The RN that can communicate with the OAMnotifies the OAM of the state of the attaching configuration information(step S106).

FIG. 9 is a flowchart related to the operation when the RN attaches tothe network and notifies the OAM of the state of the attachingconfiguration information in the first embodiment. The operation shownin FIG. 9 is started by searching for the eNB to which the RN canattach.

In step S201, when the eNB to which the RN can attach can be detected(Yes in step S201), the RN transmits an RRC connection configurationrequest to the detected eNB (step S202), and the process shifts to stepS203. When the eNB to which the RN can attach cannot be detected (No instep S201), the RN terminates the operation without notifying the OAM ofthe state of the attaching configuration information. In step S203, isthe RN judges whether the RN has completed the attaching to the network.When the RN has completed the attaching to the network (Yes in stepS203), the RN notifies the OAM of the state of the attachingconfiguration information (step S204), and terminates the operation.When the attaching to the network is not completed (No in step S203),the RN returns to step S203 to judge again whether the attaching to thenetwork has been completed or not.

FIG. 10 is a flowchart related to the operation in which the OAMreceives a notification of the state of the attaching configurationinformation in the first embodiment. In step S301, the OAM judgeswhether to receive the notification of the state of the attachingconfiguration information. When the OAM has received the notification ofthe state of the attaching configuration information (Yes in step S301),the OAM terminates the reception operation. When the OAM has notreceived the notification of the state of the attaching configurationinformation (No in step S301), the OAM returns to step S301 again tojudge whether the notification is received or not.

The operations of the base station 1 and the mobile station 3 aresimilar to typical operations, so the description thereof is omitted.

As described above, the relay station 2 according to this embodimentnotifies the OAM server 5 of the state of the attaching configurationinformation after the attaching to the network via the base station 1.This allows a communication network operator to judge whether thecontents of the attaching configuration information are appropriate ornot, without the need to go to the installed location of the relaystation 2, and to easily perform the setting of the attachingconfiguration information, such as a correction of a mismatch in theattaching configuration information or a change into correct contents.Moreover, the communication network operator can expect a reduction ininstallation operation cost due to simplification of the setting of theattaching configuration information.

Second Embodiment

In a second embodiment, when the relay station 2 cannot attach to theDeNB designated by the attaching configuration information, the relaystation 2 attaches to another eNB and notifies the OAM of a validity ofthe attaching configuration information. A valid state of the attachingconfiguration information corresponds to the case where the relaystation 2 can normally attach to the donor base station designated bythe held attaching configuration information. On the other hand, aninvalid state of the attaching configuration information corresponds tothe case where the relay station 2 cannot normally attach to the donorbase station designated by the held attaching configuration information.Specific examples of the case where the relay station cannot normallyattach to the DeNB designated by the attaching configuration information(in other words, the attaching is unsuccessful) include the case wherethe DeNB designated by the attaching configuration information is notpresent in the vicinity of the relay station 2, and the case where theattaching to the DeNB designated by the attaching configurationinformation is rejected. The notification of the validity of theattaching configuration information may include information indicatingwhether the attaching configuration information is valid or not, orinformation indicating that the attaching to the DeNB designated by theattaching configuration information is unsuccessful. The notificationmay also include information capable of determining whether the basestation to which the relay station actually attaches corresponds to thedonor base station to which the relay station should attach.

A specific example of a procedure for notifying the validity of theattaching configuration information in the second embodiment will bedescribed below with reference to FIGS. 11A, 11B, and 12.

FIGS. 11A and 11B are sequence diagrams showing an example of theprocedure for notifying the validity of the attaching configurationinformation in the second embodiment. In FIGS. 11A and 11B, “eNB 1”corresponds to a base station that is described in the attachingconfiguration information, “eNB 2” corresponds to a base station that isnot described in the attaching configuration information, “RN”corresponds to the relay station 2, “OAM” corresponds to the OAM server5, and “MME” corresponds to the core network 4. The RN can detect theeNB 2 by searching. In step S401, the RN judges whether the eNB 1 can bedetected or not based on the attaching configuration information. Whenthe eNB 1 has been detected, the operations of steps S402, S102 to S105,and S403 to S404 (Alt1 in FIG. 11A) are carried out. When the eNB 1 hasnot been detected, the operations of steps S405 and S101 to S106 (Alt2in FIG. 11B) are carried out.

When the RN has detected the eNB 1 based on the attaching configurationinformation in step S402, the RN transmits the RRC connectionconfiguration request to the detected eNB, and attaches to the network.Steps S102 to S105 showing the series of operations are similar to thoseof the first embodiment, so the detailed description thereof is omitted.Upon completion of the attaching to the network, the RN starts theoperation of an RN cell (step S403) and starts accepting an attachrequest from an RN-UE (step S404).

When the RN has not detected the eNB 1 based on the attachingconfiguration information in step S405, the RN searches for an eNB towhich the RN can attach, transmits the RRC connection configurationrequest to the detected eNB 2, and performs the operation to notify theOAM of the validity of the attaching configuration information. StepsS101 to S106 showing the series of operations are similar to those ofthe first embodiment, so the detailed description thereof is omitted.

FIG. 12 is a flowchart related to the operation in which the relaystation 2 attaches to the network and notifies the OAM of the validityof the attaching configuration information in the second embodiment. Inresponse to the operation to detect the DeNB based on the held attachingconfiguration information, the relay station 2 starts processingillustrated in the flowchart of FIG. 12. In step S501, the relay station2 judges whether the DeNB can be detected or not based on the heldattaching configuration information. When the DeNB has been detectedbased on the attaching configuration information (Yes in step S501), therelay station 2 configures the RRC connection to the detected DeNB, andattaches to the network. After transmission of the RRC connectionrequest (step S202), it is determined whether the response to the RRCconnection request is a negative response or not (step S503). When theresponse to the RRC connection request is a negative response (Yes instep S503), the process proceeds to step S502 which is described later.When the response to the RRC connection request is a positive response(No in step S503), it is determined whether the attaching to the networkhas been completed or not (step S203).

When the RN has not completed the attaching to the network (No in stepS203), the process returns to step S503 again to determine the responseto the RRC connection request. After the attaching to the network (Yesin step S203), the relay station 2 starts the operation of the RN cell(step S504). When the DeNB has not been detected based on the attachingconfiguration information (No in step S501) or when a negative responsehas been received (Yes in step S503), the relay station 2 startsdetection of another eNB which is different from the eNB designated inthe attaching configuration information (step S502). After that, therelay station 2 judges the detection result, configures the RRCconnection to the detected eNB, and notifies the OAM server of thevalidity information of the attaching configuration information afterthe attaching to the network. Steps S201 to S204 showing these series ofoperations are similar to those of the first embodiment, so the detaileddescription thereof is omitted.

A flowchart related to the operation in which the OAM server 5 receivesthe notification of the validity of the attaching configurationinformation in this embodiment is similar to that of the firstembodiment, so the detailed description is omitted. Further, theoperations of the base station 1 and the mobile station 3 are similar totypical operations, as with the first embodiment, so the descriptionthereof is omitted.

As described above, when the relay station 2 according to thisembodiment cannot find the base station to which the relay stationshould attach based on the attaching configuration information, therelay station 2 attaches to the network via another base station whichis different from the base station designated by the attachingconfiguration information, and notifies the OAM server 5 of the validityof the attaching configuration information. Accordingly, even when theDeNB setting is erroneously made in the attaching configurationinformation preliminarily set to the relay station 2, the OAM server 5can find the error without the need for the operator to directly go tothe installed location of the relay station 2. This allows acommunication network operator to judge whether the contents of theattaching configuration information are appropriate or not and to easilyperform the setting of the attaching configuration information, such asa correction of a mismatch in the attaching configuration information ora change into correct contents.

Third Embodiment

In a third embodiment, when the relay station 2 does not hold theattaching configuration information, the relay station 2 temporarilyattaches to a base station which is detected by searching and to whichthe relay station can attach. Then, the relay station 2 notifies the OAMserver 5 of information indicating that the attaching configurationinformation is not held, or of a request for the attaching configurationinformation, and acquires the attaching configuration information fromthe OAM server 5. Further, the relay station 2 re-attaches to the DeNBbased on the newly obtained attaching configuration information.

A specific example of a procedure for notifying the state (i.e.,availability) of the attaching configuration information in the thirdembodiment will be described below with reference to FIGS. 13 to 15.FIG. 13 is a sequence diagram showing an example of a procedure fornotifying the availability of the attaching configuration information inthe third embodiment. In FIG. 13, “eNB 1” corresponds to a base stationwhich is detected by searching and to which the relay station canattach, “eNB 2” corresponds to a base station described in the updatedattaching configuration information, “RN” corresponds to the relaystation 2, “OAM” corresponds to the OAM server 5, and “MME” correspondsto the core network 4.

In FIG. 13, steps S101 to S106 are similar to those of the firstembodiment, so only the differences will be described. After receivingthe notification as to the availability of the attaching configurationinformation from the RN, the OAM determines the attaching configurationinformation to be set to the RN (step S601), and sends it to the RN(step S602). The RN re-attaches to the network based on the attachingconfiguration information. The series of operations are similar to stepsS102 to S105 of the first embodiment, so the description thereof isomitted.

FIG. 14 is a flowchart related to the operation in which the relaystation 2 that does not hold the available attaching configurationinformation attaches to the network, notifies the OAM server 5 of theavailability of the attaching configuration information, and acquiresthe attaching configuration information in the third embodiment. StepsS201 to S204 are similar to those of the first embodiment, so only thedifferences will be described. In step S204, after notifying the OAMserver 5 of the availability of the attaching configuration information,the relay station 2 shifts to step S701 to determine the reception ofthe attaching configuration information. Examples of the notification ofthe availability of the attaching configuration information may includea notification indicating that the available attaching configurationinformation is not held, a notification of information on the basestation temporarily connected, and a notification for requesting newattaching configuration information.

When the attaching configuration information is received from the OAMserver 5 in step S701 (Yes in step S701), the relay station 2 configuresthe RRC connection to the new DeNB based on the newly obtained attachingconfiguration information, and performs the operation of attaching tothe network. The series of operation steps S202 to S203 are similar tothose of the first embodiment, so the detailed description thereof isomitted. After the attaching to the network, the relay station 2 startsthe operation of the RN cell (step S702), and terminates the operation.When the attaching configuration information is not received from theOAM server 5 (No in step S701), the relay station 2 terminates theoperation.

FIG. 15 is a flowchart related to the operation in which the OAM server5 receives the notification of the availability of the attachingconfiguration information and sends the attaching configurationinformation to the RN in the third embodiment. Step S301 is similar tothat of the first embodiment, so only the differences will be described.When the notification as to the availability of the attachingconfiguration information is received from the relay station 2 (Yes instep S301), the OAM server 5 determines the attaching configurationinformation to be set to the relay station 2, sends it to the relaystation 2 (step S801), and terminates the operation.

The operations of the base station 1 and the mobile station 3 aresimilar to typical operations, as with the first embodiment, so thedescription thereof is omitted.

As described above, the relay station 2 according to this embodimentacquires the updated attaching configuration information from the OAMserver after the establishment of the attaching to the network via thebase station. Then, the base station 2 re-attaches to the base stationbased on the updated attaching configuration information. Accordingly,there is no need to preliminarily set the attaching configurationinformation to the relay station 2. This makes it possible to easily setthe attaching configuration information to the relay station 2 and toreduce the man-hour required for an installer. As a result, thecommunication network operator can expect a reduction in installationoperation cost.

Fourth Embodiment

In a fourth embodiment, when the relay station 2 cannot attach to theDeNB based on attaching configuration information, the relay station 2temporarily attaches to another eNB and acquires the updated attachingconfiguration information from the OAM server 5. Then, the relay station2 re-attaches to the DeNB based on the updated attaching configurationinformation.

A specific example of a procedure for notifying the validity of theattaching configuration information in the fourth embodiment will bedescribed below with reference to FIGS. 16A, 16B, and 17. FIGS. 16A and16B are sequence diagrams showing an example of a procedure fornotifying the validity of the attaching configuration information in thefourth embodiment. In FIGS. 16 A and 16B, “eNB 1” corresponds to a basestation described in the attaching configuration information beforeupdating; “eNB 2” corresponds to a base station which is not describedin the attaching configuration information and is detected by searchingand to which the relay station can attach; “eNB 3” corresponds to a basestation described in the updated attaching configuration information;“RN” corresponds to the relay station 2; “OAM” corresponds to the OAMserver 5; and “MME” corresponds to the core network 4. The RN can detectthe eNB 2 by searching.

Steps S101 to S106, S401 to S405, and S601 to S602 are similar to thoseof the first, second, or third embodiment, so only the differences willbe described. The RN receives the attaching configuration information instep S901 of FIG. 16B, configures the RRC connection to the eNB 3 basedon the received attaching configuration information, and re-attaches tothe network.

FIG. 17 is a flowchart related to the operation in which when the relaystation 2 cannot attach to the DeNB based on the attaching configurationinformation, the relay station 2 attaches to another eNB which isdifferent from the eNB described in the attaching configurationinformation, and the OAM server 5 updates the attaching configurationinformation in the fourth embodiment. The relay station 2 startsprocessing illustrated in the flowchart of FIG. 17 in response to theoperation of detecting the DeNB based on the held attachingconfiguration information. Steps S201 to S204 and S501 to S504 aresimilar to those of the first embodiment or the second embodiment, soonly the differences will be described.

In step S204, the relay station 2 notifies the OAM server 5 of thevalidity of the attaching configuration information, and shifts to stepS1001 to judge whether the updated attaching configuration informationis received or not. When the updated attaching configuration informationis received (Yes in step S1001), the relay station 2 configures the RRCconnection to the DeNB based on the attaching configuration information(step S202). After the attaching to the network, the relay station 2starts the operation of the RN cell (step S1002), and terminates theoperation. On the other hand, when the updated attaching configurationinformation is not received (No in step S1001), the relay station 2returns to step S1001 to judge whether the updated attachingconfiguration information is received or not.

A flowchart related to the operation in which the OAM server 5 receivesthe notification as to the validity of the attaching configurationinformation is similar to that of the third embodiment, so the detaileddescription thereof is omitted. The operations of the base station 1 andthe mobile station 3 are similar to typical operations, as with thefirst embodiment, so the description is omitted.

As described above, the relay station 2 according to this embodimentsearches for a base station to which the relay station can attach, basedon the preliminarily set attaching configuration information. When thebase station cannot be detected, the relay station attaches to thenetwork via another base station, and acquires the updated attachingconfiguration information from the OAM server. The relay station 2according to this embodiment performs the attaching operation againbased on the updated attaching configuration information, and attachesto the base station described in the attaching configurationinformation. Accordingly, even when the setting of the base station iserroneously made in the preliminarily set attaching configurationinformation, the man-hour required for the installer to update theattaching configuration information held by the relay station 2 can bereduced and the updating can be facilitated. As a result, thecommunication network operator can expect a reduction in installationoperation cost.

Fifth Embodiment

In a fifth embodiment, when the RN attaches to the DeNB based on theattaching configuration information, the RN notifies the DeNB of anindication indicating the RN mode is supported. When the RN temporarilyattaches to the eNB, the RN does not notify the DeNB of the indicationindicating that the RN mode is supported.

A specific example of a procedure for notifying the validity of theattaching configuration information in the fifth embodiment will bedescribed below with reference to FIGS. 18A, 18B, and 19.

FIGS. 18A and 18B are sequence diagrams showing an example of aprocedure for notifying the validity of the attaching configurationinformation in the fifth embodiment. In FIGS. 18A and 18B, “eNB 1”corresponds to a base station described in the attaching configurationinformation; “eNB 2” corresponds to a base station that is not describedin the attaching configuration information; and “RN” corresponds to therelay station 2. The RN can detect the eNB 2 by searching.

Steps S101 to S106 and S401 to S405 are similar to those of the firstembodiment or the second embodiment, so only the differences will bedescribed. In step S1101, the RN configures the RRC connection to thedetected eNB 1 based on the attaching configuration information. At thistime, the message to configure the RRC connection includes theindication indicating that the RN mode is supported. After completion ofthe process for the RN to attach to the network, the eNB 1 configures abackhaul link (step S1102), and the RN is switched from the UE mode tothe RN mode (step S1103) and starts the operation of the RN cell (stepS104). In step S1105, the RN configures the RRC connection to the eNB 2which is different from the eNB 1 designated in the attachingconfiguration information. At this time, the RN does not include, to themessage, the indication indicating that the RN mode is supported.

FIG. 19 is a flowchart related to the operation of notifying theindication indicating that the RN mode is supported, in the process inwhich the relay station 2 according to the fifth embodiment attaches tothe network. Steps S201 to S204 and S501 to S504 are similar to those ofthe first embodiment or the second embodiment, so only the differenceswill be described.

In step S1201, the relay station 2 sends a message to configure the RRCconnection, which does not include the indication indicating that the RNmode is supported, in order to temporarily connect to an eNB other thanthe DeNB designated in the attaching configuration information. On theother hand, in step S1202, the relay station 2 sends a message toconfigure the RRC connection, which includes the indication indicatingthat the RN mode is supported, to the DeNB designated in the attachingconfiguration information, and shifts to S1203 to judge whether backhaullink configuration information is received or not, after the completionof the attaching to the network. When the backhaul link configurationinformation is received (Yes in step S1203), the relay station 2 startsthe operation of the RN cell (step S503). When the backhaul linkconfiguration information is not received (No in step S1203), the relaystation 2 returns to step S1203 to judge whether the backhaul linkconfiguration information is received or not.

FIG. 20 is a flowchart showing an example of the operation procedure ofthe base station 1 according to the fifth embodiment. Referring to FIG.20, the base station 1 starts processing illustrated in the flowchart inresponse to the reception of the RRC connection configuration requestfrom the relay station 2.

In step S1301, the base station 1 judges whether the RRC connectionconfiguration request is received or not. When the RRC connectionconfiguration request is received (Yes in step S1301), the base station1 shifts to step S1302 to judge whether the RRC connection configurationrequest includes the indication indicating that the RN mode issupported. When the RRC connection configuration request is not received(No in step S1301), the base station 1 returns to step S1301 to judgewhether the RRC connection configuration request is received or not.When the RRC connection configuration request received by the basestation 1 includes the indication indicating that the RN mode issupported (Yes in step S1302), the base station 1 sets the RRCconnection to the relay station 2 (step S1303), notifies the relaystation 2 of the backhaul link configuration information (step S1304),and terminates the operation. In step S1302, when the indicationindicating that the RN mode is supported is not included in the RRCconnection configuration request (No in step S1302), the base station 1sets the RRC connection to the relay station 2 (step S1305) andterminates the operation.

A flowchart related to the operation in which the OAM server 5 receivesthe notification as to the validity of the attaching configurationinformation is similar to that of the first embodiment, so thedescription thereof is omitted. The operations of the base station 1 andthe mobile station 3 are similar to typical operations, as with thefirst embodiment, so the description thereof is omitted.

This embodiment illustrates an example in which the base station 1judges whether the switching to the RN mode can be made or not, based onwhether the relay station 2 includes the indication indicating that theRN mode is supported. However, the RN may send a different indicationwhen the RN mode is not supported from the indication indicating thatthe RN mode is supported.

The description of the above-mentioned embodiments is made based on thesecond embodiment. However, even when the embodiments are based on anembodiment other than the second embodiment, the same effects can beobtained.

As described above, when the relay station 2 according to thisembodiment can attach to the base station based on the preliminarily setattaching configuration information, the relay station 2 notifies thebase station of the indication indicating that the RN mode is supported.On the other hand, when the relay station 2 cannot attach to the basestation based on the attaching configuration information and attaches toanother base station, the relay station 2 does not notify the basestation of the indication indicating that the RN mode is supported. Thisenables the base station 1 to set a backhaul link only to the relaystation 2 that starts the operation of the RN cell, thereby improvingthe use efficiency of the radio resource of the backhaul link.

Other Embodiment

In the case of E-UTRAN (LTE), the relay station 2 (hereinafter “relaynode”) may use one of the following two cell selection procedures.

(1) Temporal Cell Selection

This procedure requires no attaching configuration information(hereinafter “donor cell information”) in the relay node. The relay nodescans all radio channels in the E-UTRA (Evolved-UMTS Terrestrial RadioAccess) band by the function of each relay node for searching for anappropriate cell. Each relay node needs to search for only the cell thatis strongest in each frequency carrier. When the appropriate cell isfound, the cell is selected, the relay node notifies the E-UTRAN(Evolved-UMTS Terrestrial Radio Access Network) that the donor cellinformation is not held.

(2) Cell Selection Using the Held Donor Cell Information

This procedure requires donor cell information obtained from previouslyconfigured donor cell information or previously downloaded donor cellinformation, and requires, as needed, information on a cell parameter.Once the relay node finds the appropriate cell, the relay node selectsthe cell. When no appropriate cell is found or when the relay stationcannot attach to the selected cell, a temporal cell selection procedureis started.

The first to fifth embodiments of the invention described above haveillustrated the case where the present invention is applied to thenetwork that supports the RN of the LTE system. However, the applicationof the present invention is not limited to the base station thatsupports the RN of the LTE system. That is, the present invention can beapplied to any case, as long as a relay station connected to a basestation wirelessly or via a fixed line is provided and data transferredby the base station is terminated at the relay station.

Further, the processing related to the notification as to the state ofthe attaching configuration information by the relay station 2 describedin the above-mentioned first to fifth embodiments of the invention maybe implemented by causing a computer, such as a microprocessor, toexecute one or more programs. This program can be stored and provided toa computer using any type of non-transitory computer readable media.Non-transitory computer readable media include any type of tangiblestorage media. Examples of non-transitory computer readable mediainclude magnetic storage media (such as flexible disks, magnetic tapes,hard disk drives, etc.), optical magnetic storage media (e.g.magneto-optical disks), CD-ROM (Read Only Memory), CD-R, CD-R/W, andsemiconductor memories (such as mask ROM, PROM (Programmable ROM), EPROM(Erasable PROM), flash ROM, RAM (random access memory), etc.). Theprogram may be provided to a computer using any type of transitorycomputer readable media. Examples of transitory computer readable mediainclude electric signals, optical signals, and electromagnetic waves.Transitory computer readable media can provide the program to a computervia a wired communication line, such as electric wires and opticalfibers, or a wireless communication line.

The first to fifth embodiments of the invention can be arbitrarilycombined. Further, the present invention is not limited to theembodiments described above, and can be modified in various mannerswithout departing from the scope of the present invention describedabove.

This application is based upon and claims the benefit of priority fromJapanese patent application No. 2010-174455, filed on Aug. 3, 2010, thedisclosure of which is incorporated herein in its entirety by reference.

REFERENCE SIGNS LIST

-   1, 1-1, 1-2 BASE STATION-   2 RELAY STATION-   3 MOBILE STATION-   4 CORE NETWORK-   5 OAM SERVER-   10 BASE STATION CELL (eNB CELL)-   11 RADIO COMMUNICATION UNIT-   12 TRANSMIT DATA PROCESSING UNIT-   13 RECEIVED DATA PROCESSING UNIT-   14 COMMUNICATION UNIT-   15 RELAY NODE CONTROL UNIT-   20 RELAY STATION CELL (RN CELL)-   21 LOWER RADIO LINK COMMUNICATION UNIT-   22 TRANSMIT DATA PROCESSING UNIT-   23 RECEIVED DATA PROCESSING UNIT-   24 UPPER RADIO LINK COMMUNICATION UNIT-   25 ATTACHING CONFIGURATION INFORMATION CONTROL UNIT-   31 RADIO COMMUNICATION UNIT-   32 RECEIVED DATA PROCESSING UNIT-   33 TRANSMIT DATA CONTROL UNIT-   34 TRANSMIT DATA PROCESSING UNIT-   35 BUFFER UNIT-   51 COMMUNICATION UNIT-   52 TRANSMIT DATA PROCESSING UNIT-   53 RECEIVED DATA CONTROL UNIT-   54 ATTACHING CONFIGURATION INFORMATION MANAGEMENT UNIT

The invention claimed is:
 1. A base station apparatus comprising: aradio communication unit configured to perform radio communication witha user equipment (UE), a first relay node (RN), and a second RN; acontrol unit which controls communication with the first RN and thesecond RN, wherein: when the base station apparatus receives, from thefirst RN, first information related to a first RRC (Radio ResourceControl) connection, and the first information does not include an RNindication which makes a Donor e Node B (DeNB) perform a relaycommunication, the control unit controls the radio communication unit toconnect to the first RN using a first connection mode in which the firstRN operates as a UE; when the base station apparatus receives, from thesecond RN, second information related to a second RRC connection, andthe second information includes the RN indication, the control unitcontrols the radio communication unit to connect to the second RN usinga second connection mode in which the second RN operates as a relay; andwhen the base station apparatus receives, from the first RN, the firstinformation, the control unit further controls the radio communicationunit to transmit, to the first RN, third information indicating at leasta DeNB cell to access from the first RN.
 2. The base station apparatusaccording to claim 1, wherein: when the base station apparatus receives,from the second RN, the second information, the control unit furthercontrols the radio communication unit to set up bearers between thesecond RN and the base station apparatus, wherein the bearers are usedfor relaying.
 3. A method performed by a base station apparatus incommunication with a user equipment (UE), a first relay node (RN), and asecond RN, the method comprising: when the base station apparatusreceives, from the first RN, first information related to a first RRC(Radio Resource Control) connection, and the first information does notinclude an RN indication which makes a Donor e Node B (DeNB) perform arelay communication, the base station apparatus connecting to the firstRN using a first connection mode in which the first RN operates as a UE;when the base station apparatus receives, from the second RN, secondinformation related to a second RRC connection, and the secondinformation includes the RN indication, the base station apparatusconnecting to the second RN using a second connection mode in which thesecond RN operates as a relay; and when the base station apparatusreceives, from the first RN, the first information, the base stationapparatus transmitting, to the first RN, third information indicating atleast a DeNB call to access from the first RN.
 4. The method accordingto claim 3, further comprising: when the base station apparatusreceives, from the second RN, the second information, the base stationapparatus setting up bearers between the second RN and the base stationapparatus, wherein the bearers are used for relaying.
 5. The basestation apparatus according to claim 1, wherein the second RN selectsthe base station from third information indicating at least a DeNB cellto access from the second RN.
 6. The base station apparatus according tothe claim 5, wherein the third information is preconfigured.
 7. The basestation apparatus according to claim 5, wherein the third information isreceived from a base station as a first connection mode in which thesecond RN operates as a UE.
 8. The base station apparatus according toclaim 1, wherein the base station is a DeNB when the base stationreceives the second information.
 9. The base station apparatus accordingto claim 8, wherein the base station is a DeNB included in thirdinformation indicating at least a DeNB cell to access from the first RN.10. The base station apparatus according to claim 1, wherein the basestation sends, to the second RN, an RRC signaling for relayingconfiguration, after the base station receiving the second informationfrom the second RN.
 11. The method according to claim 3, furthercomprising: the second RN selecting the base station from thirdinformation indicating at least a DeNB cell to access from the secondRN.
 12. The method according to claim 11, wherein the third informationis preconfigured.
 13. The method according to claim 11, wherein thethird information is received from a base station as a first connectionmode in which the second RN operates as a UE.
 14. The method accordingto claim 3, wherein the base station is a DeNB when the base stationreceives the second information.
 15. The method according to claim 14,wherein the base station is a DeNB included in third informationindicating at least a DeNB cell to access from the first RN.
 16. Themethod according to claim 3, further comprising: the base stationsending, to the second RN, an RRC signaling for relaying configuration,after the base station receiving the second information from the secondRN.